A droplet ejecting device, such as an inkjet device, is commonly provided with an ejecting head where a liquid is temporarily stored, and also with a piezoelectric element for pressurizing the liquid stored in the ejecting head. To eject a liquid from the ejecting head, a drive signal is supplied to a piezoelectric element on the basis of a drive waveform. The drive waveform refers to data prescribing a time-sequential signal level of a drive signal applied for enabling ejection of a single droplet. Accordingly, it is possible to achieve high-precision patterning by consistently ejecting a droplet that is close to a desired value.
However, if a change in temperature occurs, a change in a viscosity of a liquid to be ejected may also occur. Thus, if a drive waveform for controlling ejection of a liquid droplet remains unchanged regardless of a change in temperature, variations in a volume of a liquid droplet ejected will also occur. Namely, a decrease in temperature of a liquid may result in an increase in a viscosity of the liquid, with the result that a droplet of the liquid ejected will have decreased volume.
To solve this problem, a technique is known for detecting a liquid temperature within an ejecting head by means of a thermal sensor provided close to the ejecting head, estimating a viscosity of the liquid from the detected temperature, and determining a drive waveform on the basis of the estimated viscosity such that a volume of a droplet ejected does not essentially change. Consequently, as compared to a fixed drive waveform method, this method provides a more stable droplet output since it employs a drive waveform that is changeable on the basis of an estimated viscosity of a liquid for droplet ejection.
However, a problem exists with such a method in that a viscosity used for the determination of a drive waveform is a value that is indirectly obtained on the basis of a temperature of a liquid for droplet ejection, and therefore an actual viscosity of the liquid may not be accurately determined. Moreover, a temperature of a liquid residing in an ejecting head is not generally uniform, and detection of the liquid's temperature will also vary depending on where a thermal sensor is provided. Consequently, in the prior art method and device a volume of an ejected droplet is subject to variance, and cannot be sufficiently accurately controlled.